Method of and apparatus for removing wood particles yielded in chipboard production

ABSTRACT

A system for use in the manufacture of chipboard including a method and apparatus initially involving the use of wood particles including grinding dust, sawdust, scrap wood and similar particles normally available in operations involved in the conventional manufacture of chipboard. The particles are located in a mixing means along with an adhesive, and a compacting apparatus is provided for forming the mixture of particles and adhesive into chip-shaped compacts. These compacts are then employed with conventionally produced chips to provide the material for making the chipboard.

United States Patent Pitzer et al.

[11] 3,833,327 Sept. 3, 1974 METHOD OF AND APPARATUS FOR REMOVING WOOD PARTICLES YIELDED IN CHIPBOARD PRODUCTION Inventors: Hans-Joachim Pitzer, Heilbronn; Wolfgang B. Pietsch, Lowenstein-l-lirrweiler, both of Germany Assignee: Hutt GmbH, Leingarten, Germany Filed: Mar. 16, 1972 Appl. No.: 235,209

Foreign Application Priority Data Oct. 22, 1971 Switzerland 15430/71 us. or 425/203, 425/224, 425/237,

425/335 Int. Cl. B29c 3/02, B290 3/04 Field of Search 425/203, 204, 205, 209,

References Cited 9 UNITED STATES PATENTS 12/1923 Van Kuren 259/6 l-leygel 425/335 X 2,945,259 7/1960 Decker et al. 425/237 X 3,034,848 5/1962 King 241/3 X 3,253,303 5/1966 Bradt 425/203 X 3,269,611 8/1966 Komarek 425/237 X 3,328,843 7/1967 Murphy, Jr. et al. 425/237 X 3,541,652 11/1970 Fischer 425/203 X 3,734,659 5/1973 Harris 425/237 X 3,738,785 6/1973 Reinhardt et a 425/224 Primary ExaminerRobert L. Spicer Jr. Attorney, Agent, or FirmMcDougall, Hersh & Scott [5 7] ABSTRACT A system for use in the manufacture of chipboard including a method and apparatus initially involving the use of wood particles including grinding dust, sawdust, scrap wood and similar particles normally available in operations involved in the conventional manufacture of chipboard. The particles are located in a mixing means along with an adhesive, and a compacting apparatus is provided for forming the mixture of particles and adhesive into chip-shaped compacts. These compacts arethen employed with conventionally pro- 1 duced chips to provide the material for making the chipboard.

3 Claims, 3 Drawing Figures METHOD OF AND APPARATUS FOR REMOVING WOOD PARTICLES YIELDED IN CI-IIPBOARD PRODUCTION The invention relates to a method of and apparatus for disposing of finely divided wood particles such as wood grinding dust separated from blowing or suction air streams used to collect the dust. The invention also rough press and then in a heated press, to form flat boards. The boards are then squared or trimmed to predetermined external dimensions and then taken away for ripening. Upon completion of ripening, the chipboards first have their surfaces ground, and then they are ready for storage, for dispatch or for further use.

The screening and squaring or trimming operations yield waste chips and sawdust, and grinding also yields dust. The grinding dust in particular is either sucked away from the grinding machine or blown off the board surfaces and must be separated from the blowing or suction air streams, e.g., by cyclones, since it must not be ejected to atmosphere. Grinding dust and sawdust present particular problems, since they are bulky and very rapidly accumulate to large amounts something like tons per hour of wood particles in average-sized firms. The particles, although in themselves material of high value, are unsaleable for economic further use, particularly in the case of grinding dust. Consequently, the dust is at present burned, which producesheat and air pollution, and represents a wastage of material i chipboard production.

It is an object of the invention to provide a method of and apparatus for disposing ofwood particles, more particularly grinding dust, sawdust and waste grits or chips, whereby the particles can be efficiently employed at a chipboard works.

It is a more specific object of this invention to provide a recovery technique of the type described, the applicability of which is not influenced by circumstances outside the works and which considerably reduces or completely obviates air pollution in the disposing of the particles while also eliminating waste of material in chipboard production.

These and other objects of this invention will appear hereinafter and for purposes of illustration but not of limitation, a specific embodiment of the invention is shown in the accompanying drawings in which:

FIG. 1 is a schematic illustration of mixing, feeding and compacting means employed in the production of chip blanks characterized by the features of this invention;

FIG. 2 is a perspective view of a suitable compacting roll employed in the apparatus of the invention; and,

FIG. 3 is a perspective view of a complementary compacting roll utilized in the apparatus.

According to the invention, the wood particles are mixed with adhesive (liquid glue or synthetic resin adhesive particles) and are pressed into flat chip-like compacts, blanks, or briquets, in a roller briquetting machine whose rollers are at an elevated temperature. The roller temperature, compacting pressure and the heat evolved in compression boosts the adhesive effect and accelerates curing. In chipboard production, the shaped compacts are used as a partial replacement for non-adhesive-treated chips in proportions of up to 10 to 20 percent, more particularly 15' percent in the middle layer.

As adhesives there can be used the liquid glues which are normally used in chipboard production and which are cured by heat and pressure, or powder-form urea resin adhesives. In the latter case, the roller temperature must be below the softening or melting point of the adhesive particles so that softening is just obtained in the roller nip and curing starts as soon as the pressure is reduced. Conveniently, the rollers are heated to from about to 200 C., the heating of both rollers being by means of a circulating heating medium, such as oil. The mixture of sawdust, grinding dust and adhesive is picked up by the rolls in the nip, compressed and converted .into the chip-like shaped'compacts or briquets of up to 18 mm in length, by 5-15 mm wide,by 1-5 mm in thickness.

The heat which is evolved by the conversion of energy in compression and which is further increased by heat exchange with the hot rollers, joins the particles together. Since' no further energy is suppliedafter the material has left the pressing zone, i.e., the narrowest part of the roller nips, the bonding agent sets and so the chip-like shaped compacts or briquets are produced immediately and can be returned to the chipboard manufacturing process. Roller temperature should therefore just be high enough to permit immediate further use of the shaped members after they have left the nip. Surprisingly, roller temperature, which is considerably above the ambient temperature, helps to prevent the material being treated from sticking to the rollers.

The glue, binding agent, or synthetic resin is preferably mixed with the sawdust, grinding dust or the like in a continuously operating mixer, Centrifugal mixers (turbo-mixers) are very suitable. Also, before being given pressure treatment at the nip of the rollers, the mixture can be given preliminary compression and air removal treatment by means of a screw,'preferably located in a chamber operating under reduced pressure. Consumption of adhesive is less, and the obtainable strength of the compacts is greater, as the air content of the mixture entering'the roller nip is decreased. An exhauster screw arrangement provides an up to 50 percent reduction of adhesive consumption.

The hardness or flexibility of the chip-like shaped compacts can be controlled by varying the ratio of ingredients in the mixture of sawdust, grinding dust and adhesive. Advantageous adhesive contents are between 5 and 15 percent, more particularly 8 and 12 percent. Optimum values can readily be discovered by experimenting in the light of the required end-product properties and of the propertiesof the feed chips. In'the choice of adhesives, consideration must be-given to the glues or synthetic resins used for the grit and dust and to the temperatures at which the chips are compressed into chipboards.

An apparatus for performing the method according to the invention has a mixer, more particularly a continuous mixer, for the wood particles (sawdust, grinding dust and possibly fibrous grit or chip particles) and the adhesive, and a roller briquetting machine having heatable briquetting rollers. As'a rule, the briquetting machine has one grooved or fluted roller and one roller formed with engraved chip-like or briquet shaped recesses. Another form of briquetting machine, which can be used in accordance with the kind of mixing, has briquet-shaped pockets in both rollers.

Preferably, an agitator which has conveying convolutions and which conveys the mixture into-the nip zone between the rollers is provided in the machine funnel. Advantageously, the mixer is a continuous centrifugal mixer or turbo-mixer. An exhausting screw can be provided in a known manner, to pre-compress the mixture and remove air from it, between the mixer and the machine, more particularly the funnel thereof.

The underlying idea of the invention, therefore, is to use more particularly a specially designed and equipped roller briquetting machine to convert into chip-like blanks or compacts the grinding dust and sawdust, etc., evolved in chipboard manufacture and to return the blanks directly to the manufacturing process, i.e., to use the blanks to form chipboards. All air pollution is obviated. Blanks measuring approximately 13 X 13 X 3 mm consisting of two-thirds grinding dust and one-third chip screenings and bonded by on the average lO percent of urea resin or phenol resin adhesive can be stored for 1 to 4 days in plastic bags, can be added in a proportion on the average of about 15 percent to fresh chips for board production and do not impair the transverse tensile strength and swelling of the finished chipboards as compared with chipboards produced using only fresh chips.

The invention and advantageous details thereof will be described in greater detail with reference to an embodirnent illustrated in the accompanying drawing.

Sawdust, residue and grinding dust evolved in chipboard production are added together with an adhesive to a continuous turbo-mixer l and mixed intensively therein. Following the mixer 1 is an exhauster screw 2 formed as a dispensing or metering screw. The screw operates within a double wall 4, and a negative pressure is produced in the outer section 5 of this double wall. The negative pressure operates through the inner perforate wall 6, which has a filter covering, into the screw zone where the mixture to be compressed is disposed. As it passes through the screw 3 some of the air in the loose-fill mixture is removed. The conveying movement re-orients the particles of material so that the particles take up a correspondingly small space when they next come into contact with atmosphere. Exhausting screws of this type are known and should be used in all cases where very fine powdery materials having ,a large air content are being dealt with, for in such cases the mixture typically has too large an air content.

Screw 3 delivers material directly to the funnel 7 of a roller briquetting machine 8. Through .the agency of a feed screw 9, which has convolutions l0'and agitating arms 11 which convey the mixture downwards, the mixture is brought to the roller nip region. The screw operates in the center of the conical funnel 7 by means of a drive motor (not shown Of the two rollers 12 and 13, the left-hand roller 12 is smooth or has just slight transverse grooving, for improved feeding of the mixture. The other (right-hand) roller 13 is engraved with shallow rectangular briquet pockets of the size of the required chip shaped members. The two rollers l2, 13 are heated in a known manner by circulating oil to about 200 C., for example by introducing oil through pipe 16 and withdrawing oil through pipe 18. The temperature depends of course upon the particular adhesive used. The mixture in the roller nip is compressed and converted into chip shaped compacts or briquets which leave the machine at the bottom, whereafter the compacts or briquets are mixed with adhesive and used together with wood chips for chipboard production. In chipboard production, the blanks prepared in accordance with the invention are mixed with the fresh wood chips, more particularly those for use in the central zone of the subsequent chipboards.

It will be understood that various changes and modifications may be made in the above described invention without departing from the spirit thereof, particularly as set forth in the following claims.

That which is claimed is: v

1. An apparatus for preparing compacts for use as additive material in the manufacture of chipboard and the like wherein wood particles comprising one or more of the members from the group consisting of grinding dust, sawdust, and scrap wood, are included in the compacts, said apparatus including a mixing means for mixing an adhesive with the particles, a compacting apparatus including briquetting rolls, feeding means positioned adjacent an outlet for the mixing means for feeding the mixture of particles and adhesive to the briquetting rolls, said feeding means comprising a funnel and a feed screw having conveying convolutions extending adjacent the nip of the briquetting rolls, means for heating the briquetting rolls to a temperature between and 200 C., said briquetting rolls including at least one roll having chip-shaped briquet recesses engraved therein, said recesses having a length up to about 18 mm, a width between about 5 and 15 mm, and a depth for producing compacts from about 1 to 5 mm in thickness, and means for continuously driving said rolls whereby said mixture is passed between the rolls and formed into said compacts.

2. An apparatus in accordance with claim 1 including agitating arms associated with the feed screw for acting on the mixture of particles and adhesive during feeding to the briquetting rolls.

3. An apparatus in accordance with claim 2 including additional compacting means'located intermediate the mixing means and said feed screw, said additional compacting means including a chamber confining a conveying screw, and means for maintaining a reduced pressure within the chamber wherebyan amount of air is removed from the mixtureof particles and adhesive. 

1. An apparatus for preparing compacts for use as additive material in the manufacture of chipboard and the like wherein wood particles comprising one or more of the members from the group consisting of grinding dust, sawdust, and scrap wood, are included in the compacts, said apparatus including a mixing means for mixing an adhesive with the particles, a compacting apparatus including briquetting rolls, feeding means positioned adjacent an outlet for the mixing means for feeding the mixture of particles and adhesive to the briquetting rolls, said feeding means comprising a funnel and a feed screw having conveying convolutions extending adjacent the nip of the briquetting rolls, means for heating the briquetting rolls to a temperature between 150* and 200* C., said briquetting rolls including at least one roll having chip-shaped briquet recesses engraved therein, said recesses having a length up to about 18 mm, a width between about 5 and 15 mm, and a depth for producing compacts from about 1 to 5 mm in thickness, and means for continuously driving said rolls whereby said mixture is passed between the rolls and formed into said compacts.
 2. An apparatus in accordance with claim 1 including agitating arms associated with the feed screw for acting on the mixture of particles and adhesive during feeding to the briquetting rolls.
 3. An apparatus in accordance with claim 2 including additional compacting means located intermediate the mixing means and said feed screw, said additional compacting means including a chamber confining a conveying screw, and means for maintaining a reduced pressure within the chamber whereby an amount of air is removed from the mixture of particles and adhesive. 